(1) Field of the Invention
The present invention relates to substrate spin treating apparatus for treating substrates, such as semiconductor wafers, glass substrates for liquid crystal displays, or glass substrates for photomasks, by supplying a photoresist solution, cleaning liquid, etching solution or other treating liquid to substrate surfaces while spinning the substrates. More particularly, the invention relates to a substrate holder for such a substrate spin treating apparatus for supporting a substrate horizontally and slightly above a turntable on which the substrate is placed.
(2) Description of the Related Art
Substrate holders for spin treating apparatus of the type noted above are disclosed in Japanese Patent Publication (Unexamined) No. 1993-90238 and Japanese Utility Model Publication (Unexamined) No. 1992-65446, for example.
This type of substrate holder includes a plurality of substrate support pins which project above an upper surface of a turntable on which a substrate is placed. These support pins support the substrate while maintaining edges of the substrate in place. With such a substrate holder, the substrate is supported slightly above the upper surface of the turntable, to avoid damage and contamination of the lower surface or reverse side of the substrate which would occur if the substrate were placed in contact with the turntable. However, mist formed by scattering of the treating liquid during a treating operation could drift under the substrate and adhere to the reverse side thereof, thereby contaminating the lower surface of the substrate. To prevent the mist from drifting to the reverse side of the substrate, what is known as back-rinsing is carried out in which pure water or the like is sprayed to the reverse side during a spin treatment.
The conventional construction noted above has the following drawbacks. That is in a photoresist coating process, for example, the mist adhering to the reverse side of the substrate hardens thereon if the above back-rinsing fails to keep the mist away from the reverse side effectively. In an exposure process to follow, for example, the upper surface or reverse side of the substrate has a subtly varying height due to different thicknesses of the solids formed of hardened mist on the reverse side. This causes exposure optics to be defocused, thereby making it impossible to expose a pattern on the substrate surface properly. Therefore, in, some cases, the substrate is cleaned prior to the exposure process to remove the solids from the reverse side of the substrate.
In the cleaning operation, the substrate is supported by the spinning holder, with the obverse side thereof carrying the photoresist facing downward. The substrate is spun in this state and the reverse side of the substrate is cleaned with a cleaning brush or high pressure water jet applied thereto.
As noted above, back-rinsing may be carried out at this time in order to prevent mist of the cleaning liquid from adhering to the obverse side (photoresist film) of the substrate facing downward. However, this could damage the photoresist film formed on the obverse side of the substrate.
If the reverse side is cleaned without the back-rinsing to avoid damage to the photoresist film, then the mist will adhere to the photoresist film on the obverse side of the substrate. It is extremely difficult to remove the mist adhering to the photoresist film later on.
On the other hand, it is conceivable to reduce the height of the substrate support pins arranged on the turntable to minimize the gap between the substrate and turntable, thereby preventing mist from entering the gap. However, such a construction would make it difficult to employ an ordinary substrate transport mechanism with a transport arm for suction-supporting a substrate and entering a space corresponding to the gap between the turntable and the lower surface of the substrate, to transfer the substrate onto the support pins. Thus, a special substrate transport mechanism would be required if the support pins were reduced in height.